Monolithic nanocarbon-based
CO2 solid sorbents offer fast mass transport, easy handling,
minor pressure
drop, and cycle operation stability because of the interconnected
three-dimensional network of pores that provides a unique porous structure.
In this work, following a one-step water-based method, graphene-based
monoliths were produced by a spontaneous reduction-induced self-assembly
of graphene oxide nanoplatelets under mild conditions (45–90
°C). By varying the reaction temperature and amount of reducing
agent (ascorbic acid, AsA), the engineering of the porous structure
of the monoliths was performed and resulted in a portfolio of different
monoliths with different capacities for CO2 adsorption.
It was found that the monolith produced at the highest temperature
and with the lowest AsA amount possessed the highest specific surface
area and porosity as well as a high level of functionalization. As
a result, this monolith presented an excellent CO2 capture
performance of 2.1 mmol/g at T = 25 °C and P = 1 atm. This value is between the highest achieved in
CO2 sorption in comparison to that of similar and nontreated
materials. The selectivity of this monolith for CO2 capture
over that for N2 at 25 °C and atmospheric pressure
is 53, presenting a high viability for practical applications. The
monolith was shown to lose capacity in cycle operations, probably
because of the collapse of the smallest pores, which was solved by
the addition of a small amount of polymer particles during the one-step
synthesis of the monolithic structures. This modification provides
for an excellent stability over five adsorption/desorption cycles.
Polymer composite materials with hierarchical porous structure have been advancing in many different application fields due to excellent physico-chemical properties. However, their synthesis continues to be a highly energy-demanding and environmentally unfriendly process. This work reports a unique water based synthesis of monolithic 3D reduced graphene oxide (rGO) composite structures reinforced with poly(methyl methacrylate) polymer nanoparticles functionalized with epoxy functional groups. The method is based on reduction-induced self-assembly process performed at mild conditions. The textural properties and the surface chemistry of the monoliths were varied by changing the reaction conditions and quantity of added polymer to the structure. Moreover, the incorporation of the polymer into the structures improves the solvent resistance of the composites due to the formation of crosslinks between the polymer and the rGO. The monolithic composites were evaluated for selective capture of CO2. A balance between the specific surface area and the level of functionalization was found to be critical for obtaining high CO2 capacity and CO2/N2 selectivity. The polymer quantity affects the textural properties, thus lowering its amount the specific surface area and the amount of functional groups are higher. This affects positively the capacity for CO2 capture, thus, the maximum achieved was in the range 3.56–3.85 mmol/g at 1 atm and 25 °C.
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